The present invention relates to carbohydrate derivatives having an immunomodulating effect, pharmaceutical compositions containing the same, and use of the carbohydrate derivatives in the manufacture of a medicament for therapy.
Immunomodulators, in the following referred to as IMs, are a group of non-endogenous compounds which modulate macrophages and related cell types, thereby stimulating or down-regulating the immune defence of the body. In most cases this modulation consists of a stimulation of macrophages and related cell types.
By the term xe2x80x9cmacrophagesxe2x80x9d is meant, inter alia, cells having the capability of enclosing particles having a size of about 1-10 xcexcm and additionally affecting their environment by means of secretion of biologically active substances. The term xe2x80x9cmacrophagesxe2x80x9d also comprises related cell types, such as coelomocytes and most phagocytes of lower animals (invertebrates), promonocytes, monocytes, Kupffer cells, microglial cells, histiocytes and tissue macrophages of higher animals (vertebrates) and various types of syncytia cells and giant cells which are formed by fusion with individual macrophages.
A large number of IMs consist of carbohydrates, such as xcex21xe2x86x923-glucans and alginates (salts of polymannuronic acid), or contain carbohydrate units, such as bacterial lipopolysaccharides, LPS and peptidoglycans. Some of these compounds, for instance LPS, are toxic and consequently not suitable for use in human or veterinary medicine in those cases where an immunity-enhancing effect is desired. Other IMs, such as xcex21xe2x86x923-glucans, seem to be virtually nontoxic although they have a clear biological activity both in vitro and in vivo. As examples of pharmacological effects caused by the latter compounds mention can be made of, inter alia, strong stimulation of the production of cytokine, nitric oxide and arachidonic acid metabolites in macrophages (Seljelid, R. and Eskeland, T., Eur J. Haematol., 51, 267-275, 1993; Seljelid, R. and Busund, L.-T. R., Eur J. Haematol., 52, 1-12, 1994; Sveinbjxc3x8rnsson, B., Olsen, R., Seternes, O. M. and Seljelid, R., Biochem. Biophys. Res. Comm., 223, 643-649, 1996), resistance to lethal infections in both mammals and lower vertebrates (animals) and invertebrates (Dalmo, R. A., Bxc3x8gwald, J., Ingebrigtsen, K. and Seljelid, R., J Fish Diseases, 19, 449-457, 1996; Busund, L-T., Rasmussen and Seljelid, R., in Molecular Pathogenesis of Surgical Infections, Wadstrxc3x6m. T., Holder, I. A., Kronvall, G. (eds.), Proceedings of the Eric K. Fernstrxc3x6m Symposium, Lund, pp 293-302, 1992), regression of syngeneic tumours in mice (Seljelid, R., Bioscience Reports, 6, 845-851, 1986; Seljelid, R., Scand. J. Immunol., 29, 181-192, 1989) and prevention of metastases in experimental tumours in rats (Sveinbjxc3x8rnsson et al, in press).
In those cases where carbohydrate immunomodulators, below referred to as CIMs, have been hydrolysed in connection with the production of oligosaccharides, the biological activity in general has disappeared (Seljelid, R., Bxc3x8gwald, J. and Lundwall, xc3x85., Exp. Cell. Res., 131, 121-129, 1981; Seljelid, R. et al, Scand. J. Immunol., in press, 1997).
It is also known to modify existing CIMs while maintaining their biological activity in respect of stimulation of macrophages in vitro. Such a modification is the substitution of a hydroxyl group with an amino group (Bxc3x8gwald, J., Seljelid, R. and Hoffman. J., J. Carbohydr. Res., 148, 101-107, 1986; Rasmussen, L.-T. and Seljelid, R., Scand. J. Immunol., 32, 321-331, 1990), the resulting aminated xcex21xe2x86x923-glucan besides being found to be water-soluble contrary to the non-modified xcex21xe2x86x923-glucan. This may be caused by the fact that precisely the hydroxyl groups which are important to the aggregate formation in xcex21xe2x86x923-glucan (vide infra), which aggregate formation lowers its solubility, have been substituted by amino groups which complicate the aggregate formation, resulting in the net effect that the solubility increases significantly in said amino substitution.
U.S. Pat. No. 4,795,745 A discloses a composition in which soluble xcex21xe2x86x923-glucan has been bound to a water-insoluble carrier, which results in a composition which accomplishes activation of macrophages.
Another type of modified xcex21xe2x86x923-glucan is disclosed in JP 04-2140701 A, in which the hydroxyl groups of a xcex21xe2x86x923-glucan having a molecular weight from 200 and 800 g/mole have been etherified with both lower hydroxyalkyl groups having 2-4 carbon atoms and higher alkyl groups having 8-26 carbon atoms. These compounds are used for e.g. cosmetic and medicinal purposes.
A common denominator of the carbohydrates, and especially xcex21xe2x86x923-glucans, which are known up to now as immunomodulating substances is that their binding to receptors on the cell surfaces of macrophages and related cell types mainly occurs via hydrogen bonds. This is obvious when observing that the most important functional groups in addition to the actual carbon skeleton are either hydroxyl or amino groups, below referred to as hydrogen-binding groups, which both have the capacity of binding to, for instance, a receptor by means of hydrogen bonds. If one or more of these hydrogen-binding groups are replaced with non-hydrogen-binding groups, the binding of the compounds to the receptor or receptors will therefore probably be weakened since the substrate, i.e. the carbohydrate, loses one or more binding positions. The weakening will probably be greater, the lower hydrogen-binding capacity the substituting group presents. Moreover, steric hindrances, if any, are often important to the binding, and since both hydroxyl and amino groups from a sterical point of view are relatively unhindered groups, a sterically hindered substituent for one of these groups may weaken the binding to the receptor or receptors. As a rule, the weakening of the binding increases, the more sterically hindered the substituent is.
Summing up the above discussion, it may therefore be established that a substituent to hydroxyl or amino groups which has both a lower hydrogen-binding capacity and a larger sterical hindrance than any one of the above-mentioned groups is in the first place expected to cause a weakening of the binding of a carbohydrate to a receptor.
However, according to the present invention it has surprisingly been found that immunomodulating carbohydrates which have been etherified with aliphatic hydrocarbon chains have an immunomodulating effect and, thus, stimulate machrophages and related cell types. For these etherified immunomodulating carbohydrates, the expected weakening of the receptor binding to the macrophages has thus not occurred.
The IMs which consist of pure carbohydrates, such as xcex21xe2x86x923-glucans, alginates and agarose, are of course hydrophilic, but are all the same poorly soluble in water owing to their high molecular weight in combination with aggregate formation and intermolecular hydrogen bonds. Since these properties often reduce the general bioavailability of the compounds, this is disadvantageous for their use as pharmaceutical preparations, above all in respect of, inter alia, dosage, uptake, distribution and biological half-life in the body after administration. It is known (vide supra) that modified xcex21xe2x86x923-glucans are often more easily water-soluble than the non-modified starting material in spite of a seemingly insignificant modification of the said type of compound. It thus seems probable that also minor changes are in many cases sufficient to considerably affect, for instance, intermolecular hydrogen bonds and aggregate formation, which to a high extent cause the insignificant water solubility of many non-modified IMs.
The etherification of the compounds according to the present invention supplies an improvement of the lipophilic properties of the compounds. These new lipophilic properties affect, inter alia, dosage, uptake, distribution and biological half-life in the body after administration in a favourable manner with maintained or improved biological activity. The increased lipophilicity of the compounds according to the present invention results in their general capacity of penetrating skin being good, whereby topical administering forms are particularly advantageous owing to the improved receptivity.
An aim of the invention thus is to present a completely new class of compounds comprising etherified carbohydrates having an immunomodulating effect.
One more aim of the present invention is to provide new carbohydrate derivatives which have been etherified with one or more aliphatic hydrocarbon chains, said carbohydrate derivatives stimulating macrophages and related cell types.
A further aim of the present invention is to provide etherified carbohydrate derivatives which have more favourable preparation and administration properties than the corresponding non-etherified carbohydrates.
A still further aim of the present invention is to provide etherified carbohydrate derivatives, whose aliphatic hydrocarbon chains can be modified by further substitution or unsaturation, thereby affecting, for instance, dosage, uptake, distribution and biological half-life in a favourable manner.
Another aim of the present invention is to provide etherified carbohydrate derivatives for use as pharmaceutical preparations.
One more aim of the present invention is to provide a pharmaceutical composition comprising carbohydrate derivatives which have been etherified with one or more aliphatic hydrocarbon chains.
A further aim of the present invention is to provide use of etherified carbohydrate derivatives for the preparation of a medicament for treatment of conditions in which macrophages and related cell types are of importance.
Another aim of the present invention is to provide a method of preparing etherified carbohydrate derivatives having an immunomodulating effect.
The present invention provides new carbohydrate derivatives having an immunomodulating effect. By immunomodulating effect is understood that the new carbohydrate derivatives stimulate or down-regulate macrophages and related cell types and are usable for treatment of inflammatory, infectious or degenerative conditions.
The new carbohydrate derivatives according to the present invention have an immunomodulating effect and contain an oligo- or polysaccharide, said oligo- or polysaccharide comprising at least 5 monosaccharide units in the carbohydrate chain, preferably from 5 to 100 monosaccharide units, more preferred from 5 to 60 monosaccharide units, still more preferred from 5 to 20 monosaccharide units, even more preferred from 5 to 10 monosaccharide units, most preferred from 5 to 8 monosaccharide units, and very most preferred 6 or 7 monosaccharide units. In these carbohydrate derivatives, one or more of the hydroxyl groups are etherified with one or more identical or different aliphatic hydrocarbon chains containing at least 7 carbon atoms, preferably from 7 to 30 carbon atoms, more preferred from 12 to 22 carbon atoms, still more preferred from 16 to 20 carbon atoms, and most preferred 18 carbon atoms. The degree of etherification of these carbohydrate derivatives is about 10-90% by weight, preferably about 30-70% by weight, more preferred about 40-60%, by weight, and most preferred about 50%. The most preferred degree of etherification can also be expressed as the amount of etherified hydroxyl groups, about 50% by weight corresponding to the condition that about {fraction (2/9)} of the hydroxyl groups are etherified with aliphatic hydrocarbon chains. Moreover, these aliphatic hydrocarbon chains can optionally be further substituted with preferably one or more halogen atoms and/or protected or unprotected hydroxyl groups
The etherified carbohydrate derivatives of the invention are preferably derivatives or analogues of xcex21xe2x86x923-glucan, curdlan, alginic acid, agarose, laminaran, yeast glucan or another glucan.
A preferred embodiment of the present invention comprises an etherified carbohydrate derivative having the following general formula I: 
wherein
n is an integer in the range from 3 to 98, preferably an integer from 3 to 58, more preferred an integer from 3 to 15, still more preferred an integer from 3 to 15, even more preferred an integer from 3 to 12, yet even more preferred an integer from 3 to 10, particularly more preferred an integer from 3 to 8, even more particularly preferred an integer from 3 to 6, and most preferred n=4 or 5; and
each group R independently represents a hydrogen atom or an aliphatic hydrocarbon chain containing from 7 to 30 carbon atoms, more preferred from 12 to 22 carbon atoms, still more preferred from 16 to 20 carbon atoms, and most preferred 18 carbon atoms, said hydrocarbon chain being either saturated or unsaturated. It will be appreciated that the aliphatic hydrocarbon chain may be straight or branched. In the very most preferred embodiment, R is an n-octadecanyl group.
Besides, within the scope of the invention R can optionally be additionally substituted with preferably one or more halogen atoms and/or protected or unprotected hydroxyl groups. The degree of etherification of the preferred carbohydrate derivative according to formula I above is about 10-90% by weight, preferably about 30-70% by weight, more preferred about 40-60% by weight, and most preferred about 50%. The most preferred degree of etherification of the carbohydrate derivative according to formula I can also be expressed as the amount of etherified hydroxyl groups, about 50% by weight corresponding to the condition that about {fraction (2/9)} of the hydroxyl groups are etherified with aliphatic hydrocarbon chains.
According to the present invention there is also provided an etherified carbohydrate derivative according to the invention for use as a pharmaceutical. Thus, it may be used in pharmaceutical compositions for oral, intravenous, topical, intraperitoneal or subcutaneous administration, in association with one or more pharmaceutically acceptable carriers, diluents or adjuvants that are well known in the art.
The pharmaceutical composition of the invention may be administered topically, in the form of solutions, suspensions or systemically, e.g. by oral administration in the form of tablets, capsules, syrups, powders or granules or by parenteral administration in the form of solutions or suspensions, or by subcutaneous administration or by rectal administration in the form of suppositories or transdermally.
The amount of etherified carbohydrate derivatives per dosage unit in the pharmaceutical composition according to the present invention is within the range of from about 1 to 5,000 mg, preferably from about 10 to 1,000 mg, more preferred from about 50 to 500 mg, and most preferred from about 100 to 250 mg. A preferred pharmaceutical composition of the etherified carbohydrate derivatives according to the present invention is specifically designed for topical administration.
Besides, the present invention provides use of the etherified carbohydrate derivatives according to the invention for the manufacture of a medicament for therapeutic or prophylactic treatment. The produced medicament is particularly, although not exclusively, intended for treatment of various inflammatory and degenerative conditions.
The present invention also provides a method for medicinal treatment of immunological disorders in a human or animal patient in which macrophages and related cell types are stimulated or down-regulated, wherein a therapeutically effective amount of a carbohydrate derivative according to the invention is administered to the patient. The method for treatment particularly, although not exclusively, relates to an immunological disorder which manifests itself as an inflammatory or degenerative condition.
The present invention also provides a method for producing the new carbohydrate derivative according to the invention, comprising the step of reacting the oligo- or polysaccharide with an etherifying reagent, for example reacting the oligo- or polysaccharide with an electrophilic reagent containing an aliphatic hydrocarbon chain in a strongly basic solution in a polar solvent, preferably a polar aprotic solvent, in an inert atmosphere. In an embodiment, the oligo- or polysaccharide is curdlan, i. e. xcex21xe2x86x923-D-polyglucopyranose, and in a preferred embodiment, the oligo- or polysaccharide is xcex21xe2x86x923-D-hexaglucopyranose. According to a further embodiment, the solvent is dry dimethyl sulphoxide and the electrophilic aliphatic hydrocarbon chain is an alkyl iodide, preferably iodooctadecane. The reaction is preferably carried out in a nitrogen gas atmosphere at about 20-60xc2x0 C. for about 4-120 h. According to a preferred embodiment, the reaction is carried out at about 40xc2x0 C. for about 24-120 h.
The following non-limiting Examples illustrate the invention in more detail.